A Vuilleumier heat pump was disclosed in U.S. Pat. No. 1,275,507, filed 29 Jan. 1917. In a Vuilleumier heat pump 10, two displacers (or pistons) are provided in a cylinder 20 and defining three chambers: a hot displacer 12 between a hot chamber 22 and a warm chamber 24 and a cold displacer 16 between the warm chamber 24 and a cold chamber 26, as example of which is shown in FIG. 1. Displacers 12 and 16 reciprocate within cylinder 20 to change the volume of fluid contained in the three chambers. E.g., when hot displacer 12 is an extreme position towards hot chamber 22, most of the fluid is pushed out of hot chamber 22, through a hot heat exchanger 28. Hot heat exchanger 28 is coupled to a burner 27 that is supplied fuel and air. The fluid travels next through a hot recuperator 30, a warm heat exchanger 32, a cold recuperator 34, and a cold heat exchanger 36. Elements 28, 30, 32, 34, and 36 are fluidly coupled to cylinder 20 external to the cylinder and having a passage 38 between warm heat exchanger 32 and warm chamber 24. Displacers 12 and 16 are caused to reciprocate by a crank arrangement 40.
The movement of displacers 12 and 16 as driven by crank arrangement 40 is substantially sinusoidal, as illustrated in FIG. 2. The displacer height and their movement during reciprocation is illustrated as a function of crank angle degree in FIG. 2 and identified as D_h and D_c. The volumes between the hot and cold displacers in the 3 chambers are also illustrates in FIG. 2: V_h, V_w, and V_c. Movement of cold displacer 16 is offset from that of hot displacer 12 by a phase angle, such as 90°. Chambers 22, 24, and 26 are fluidly coupled to each other with little flow restriction. Thus, pressure in the three chambers is substantially the same, but varies as a function of time, as shown in FIG. 3. The pressure in the cylinder rises when flow through hot exchanger 28 raises the overall temperature of the gases within the closed system and the pressure within the cylinder falls when energy is extracted via warm heat exchanger 32.
A Vuilleumier heat pump is a closed thermodynamic cycle in which the working fluid, a gas, remains in the cylinders. Energy is transferred to and from the heat pump through heat exchangers. In a heating mode, energy is transferred to the hot chamber via a burner or other high temperature energy source. Energy is also transferred to the fluid in the cold heat exchanger from the environment. The energy transferred for space heating or hot water heating, as examples, is extracted from the warm chamber via a heat exchanger. Because some of the energy is extracted from the environment, the coefficient of performance substantially exceeds 1 at many operating conditions. This is in comparison to a standard furnace in which the coefficient of performance can at best approach 1 and only in furnaces in which the water vapor in the exhaust is condensed. The heat pump may also be used for cooling by energy extracted in the cold heat exchanger. Vuilleumier heat pumps have been used to develop cryogenic temperatures.
Through modeling of the system, it has been found that coefficient of performance of the system could be improved if one of the displacers could dwell at its extreme position while the other displacer moves and vice versa, rather than having both of them be in continuous movement, i.e., separated by a fixed phase angle.
To obtain reasonable performance in the Vuilleumier heat pump, the working fluid is either hydrogen or helium, which is pressurized to about 100 bar, as a non-limiting example. Pressure is fairly constant throughout the cylinder, but varies as a function of crank angle degree, as shown in FIG. 3.
Preventing leakage of either of these gases is a challenge. In prior art Vuilleumier heat pumps, the rotating crank arrangement to which the displacers are coupled may be located outside the housing such that the moving connecting rods that attach to the displacers pass through the wall of the housing. Sealing around a moving and rocking connecting rod presents a sealing challenge. Alternatively, the rotating crank arrangement is within the sealed housing yielding a heavier, bulkier heat pump.